The present invention relates to a universal H5N1 vaccine. More specifically, the present invention relates to the identification of three H5N1 strains which cover the entire variants in the neutralizing epitopes of hemagglutinin among most H5N1 lineages. The present invention further relates a universal H5N1 vaccine that comprises the three H5N1 strains or that comprises hemagglutinin peptides of each of these three strains.
The publications and other materials used herein to illuminate the background of the invention or provide additional details respecting the practice, are incorporated by reference, and for convenience are respectively grouped in the Bibliography.
Influenza virus evades immune system by randomly changing the antigenic determinants, such as the major neutralizing epitopes, present in the globular head region of hemagglutinin. Upon infection, host response is mainly characterized by the induction of antibodies against such neutralizing epitopes, which blocks the attachment of viral hemagglutinin to the target cell receptor. However, considerable amino acid variations within these neutralizing epitopes of HA lead to the emergence of antigenically distinct influenza H5N1 viruses. In fact, it has been reported that seasonal influenza viruses were able to efficiently escape from vaccine-induced immunity in human population through antigenic drift. Moreover, mutation of a few key amino acids in HA1 variable regions is sufficient to allow viral escape from vaccine-induced antibody responses. Previous attempts to identify the amino acid substitutions within HA sequences of variants escaped from neutralization by monoclonal antibodies has revealed neutralizing epitope sites of HA (Kaverin et al., 2002; Kaverin et al., 2007).
The nature of influenza virus to randomly mutate and evolve into new types with diverse antigenic determinants is an important challenge in the control of influenza infection (Plotkin et al., 2002). This has been evidently recognized by the recent outbreaks of H5N1 avian flu and the current pandemic situation with H1N1 swine-origin influenza A virus (S-OIV). In fact, it has been well documented in literature that H5N1 had acquired the ability to infect human tissues due mainly to the occurrence of mutation events (Ayora-Talayera et al., 2009). Highly pathogenic avian influenza (HPAI) H5N1 are antigenically distinguishable owing to the differences in the hemagglutinin (HA) sequences, the principal determinant of immunity to influenza, resulting in different lineages or clades of H5N1 (Lam et al., 2008; WHO, 2005). Control of infection with current H5N1 vaccines does not appear to be effective against heterologous strains or phylogenetically variant clades of H5N1 in part due to the variation in the HA sequences, particularly within the neutralizing epitope region. Since present vaccines are solely based on the induction of neutralizing antibodies against these epitopes, differences in these sequences may render the current vaccines unqualified for prevention of influenza globally. In fact, current H5N1 vaccine candidates continue to provide good antigenic coverage of most isolates within corresponding clades, it has been recently recognized that some viruses within clades 1, 2.2 and 2.3 itself shows evidence of antigenic heterogeneity.
To overcome such limitations and to completely realize the potential of vaccines worldwide, the concept of universal vaccines based on conserved viral proteins has been recently proposed. Highly conserved ion channel protein (M2) or the nucleoprotein (NP) of influenza virus has been evaluated for the induction of cross-protective cellular immunity and viral clearance (Wu et al., 2007; Chen and Subbarao, 2009). A similar approach with conserved fusion peptide of the hemagglutinin is another option to inhibit the fusion of the virus to the host cell membrane (Gerhard et al., 2006). Antibodies generated against these conserved proteins may reduce viral spread and accelerate recovery from influenza. However, antibodies specific to these proteins are poorly immunogenic and found to be infection permissive. Thus, development of vaccine based on the influenza virus hemagglutinin appears to be the only viable option to prevent infections by HPAI such as H5N1. Nevertheless, amino acid variations within the major antigenic neutralizing epitope region among the H5 subtype restricts the development of such universal vaccines against different H5N1 lineages.
Therefore, it is desired to develop a universal vaccine that provides some degree of protective immunity against different H5N1 lineages.